1. Field of the Invention
The present invention relates to a threaded cap for bottles and jars removably attached to the bottle by relative rotation.
2. Description of the Prior Art
Wide mouth bottles and jars of glass or plastic find widespread use for a variety of products due to the ease with which access to the contents may be gained and for other reasons.
Obtaining proper closure of such containers has presented problems due to the large dimensions of the opening. A number of different types of closures have been utilized. Multi-part closures, such as those commonly used for preserving jars, function adequately but are complex, expensive, and usually suited only for limited applications. For these reasons, single piece plastic or metal screw caps have come into most widespread commercial use. However, at present, such lids suffer several shortcomings.
One such shortcoming is a loosening of the lid on the jar termed "popping off". Popping off typically occurs because the necks of the wide mouth jars are often not truly round but tend to be somewhat oval. The lid thus contacts the jar at two diametrically opposed locations, while at locations 90.degree. from the contact points, a rather loose engagement is obtained. This loose engagement permitted the lid thread to ride over the jar thread and the lid to pop off. Wide helical thread forms of large pitch which complete only approximately a single revolution of engagement between the jar neck and the lid contributed to this failing, as well as to a tendency to stripping of the threaded cap when the cap is applied.
Clearances between the lid and the jar threads could be reduced to lessen popping off and to enhance the seal provided by the cap. However, reduced clearances increased the torque required to secure the lid and often prevented use of automatic capping machinery.
Earlier lids were also subject to "backing off" in which the lid tended to unscrew over a period of time as a result of plastic creep in the lid material or jar material.